1. Field of the Invention
This invention relates to a perfecting printer for separately printing both faces of individual cutforms by a single printing unit.
2. Description of the Prior Art
Perfect or two-face printing is advantageous in that it halves the total number of sheets or cutforms required to print out a given amount of information by one-face printing. Because of such an advantage, various attempts have been made to provide perfecting printers.
In one possible example, a perfecting printer employs two separate printing units respectively for printing the front and rear faces of each cutform during a single forward transfer thereof.
Another example of perfecting printer incorporates a single printing unit through which each cutform is passed twice, first with its front face directed to the printer head and next with its rear face directed thereto. A more specific arrangement of such an example is disclosed in Japanese Patent Application Laid-open No. 59-115875 (Laid-open: July 4, 1984; Filed: Dec. 23, 1982; Application No.: 57-224852; Inventor: Yutaka OGINOTANI) or in Japanese Patent Application Laid-open No. 60-257254 (Laid-open: Dec. 19, 1985: Filed: June 4, 1984: Application No.: 59-114045; Inventor: Osamu SAKAI et al) and for clarity will now be described with reference to FIG. 9 of the accompanying drawings.
Referring to FIG. 9, a prior art perfecting printer comprises a feed stacker 100 receiving a stack of cutforms or sheets 101, and a feeding roller 102 disposed above the stacker 100 for successively feeding the cutforms 101 onto a transfer path 103. A printing unit 104 is arranged at an intermediate position of the transfer path 103. Behind the printing unit 104 is a pivotal shift plate 105 for selectively directing the cutform 101 into a return-turnover path 106 or into a discharge stacker 107. The return-turnover path 106 extends substantially around the printing unit 104 and is provided with pairs of return rollers 108. Adjacent to the outlet end of the return-turnover path 106 is a re-feeding device 109 which is selectively pivotable to a first position for continuity with the return-turnover path 106 or to a second position for continuity with a guide plate 110 located immediately before the feeding roller 102.
In operation, each cutform 101 fed onto the transfer path 103 with its top edge t directed forward is advanced by a pair of transfer rollers 111. During such advance, the front face of the cutform 101 is printed from the top edge t by the printing unit 104, as illustrated in FIG. 10a. At this time, the shift plate 105 is pivoted to its lower position indicated in solid lines in FIG. 9. Thus, the cutform 101 is directed into the return-turnover path 106 after front-face printing.
Since the return path 106 extends substantially around the printing unit 104, the cutform 101 is completely turned over after it has been moved through the path 106 by the return rollers 108. The cutform 101 thus turned over is received in the re-feeding device 109 pivoted to the first position. The re-feeding device 109 is then pivoted to the second position indicated in broken lines in FIG. 9 to re-feed the cutform 101 onto the transfer path 103 by way of the guide plate 110.
The cutform 101 now with its bottom edge b directed forward is advanced along the transfer path 103. During this second forward transfer, the rear face of the cutform is printed from its bottom edge b, as shown in FIG. 10b.
Finally, the shift plate 105 is pivotally raised, and the cutform 101 is taken out into the discharge stacker 107.
Though capable of printing both faces of each cutform 101 by the single printing unit 104, the prior art printer has the following disadvantages.
According to the prior art arrangement, since the cutform 101 is transferred only in the forward direction on the transfer path 103, the inlet end of the return-turnover path 106 must be positioned behind the printing unit 104 in order to receive the cutform 101 after printing. Therefore, the return path 106 must extends substantially around or over the printing unit 104 to bring the cutform 101 back to the feed side of the printing unit 104. Such an arrangement inevitably results in a considerable increase in the overall size of the printer, thereby providing difficulty in manufacture and handling.
Further, with the prior art printer, printing on the front face of the cutform 101 is started from the top edge t, whereas printing on the rear face thereof is initiated from the bottom edge b. Such a printing manner requires complicated control of the printing unit 104 in order to provide identical margins (side margins as well as top and bottom margins) with respect to both faces of the rectangular cutform 101. Particularly, when the cutform 101 carries ruled frames 112, 112' (see FIGS. 10a and 10b) or lines (not shown) at corresponding positions on both faces thereof, variations or deviations in printing positions due to poor control of the printing unit 104 become unacceptable. In addition, a similar problem also occurs due to an unexpected slide in the movement of the cutform 101 during printing.